Project Summary Background: The gate theory of pain predicts that inhibitory interneurons in the dorsal horn act as ?gate control? elements to mediate interaction between innocuous and noxious stimuli. It has been postulated that release of this inhibitory gate allows innocuous mechanical stimuli to access the nociceptive pathway resulting in tactile allodynia following nerve injury. Increasing evidence demonstrates an excitatory pathway involving PKC?-expressing interneurons that is held silent under nonpathological conditions via a strong feedforward inhibitory gate by local interneurons. Failure of the inhibitory control on PKC?-expressing interneurons is believed to underly tactile alloynia. In the neuropathic pain state failure of the inhibitory gate is due to a BDNF- dependent reduction in inhibitory tone mediated by a change in chloride homeostasis resulting from altered expression of chloride cotransporters. Current data demonstrates that the precursor protein VGF (non- acronymic) is upregulated in the spinal cord following nerve injury, and preliminary data suggest that the VGF- derived neuropeptide TLQP-62 induces BDNF signaling in the spinal cord. Objective: We hypothesize that TLQP-62 contributes to tactile allodynia following nerve injury by mediating a BDNF-dependent central sensitization reliant on a reduction in inhibitory tone. The proposed studies will characterize this newly identified mediator of neuroplasticity and its contribution to the development of neuropathic pain. The mechanistic understanding acquired will advance our search for new therapeutic interventions and biomarkers for neuropathic pain. Specific aims: 1) Determine the function of TLQP-62 in inducing BDNF-dependent changes in chloride cotransporter expression after nerve injury, using biochemical approaches. 2) Determine the function of TLQP- 62 in the development of reduced inhibitory tone following nerve injury, patch-clamp recording and calcium imaging in spinal cord slices. 3) Determine the function of TLQP-62 in opening of the feedforward inhibitory gate, using in vivo electrophysiology.